Sputtering



Sept. 22, 1970 E. c. MULY, JR 3,530,057

SPUTTERING Filed Mayas, 1967 To PUMPS 3,530,057 SPUTTERENG Emil C. Maly,Jr., Needham, Mass., assgnor to National Research Corporation, NewtonHighlands, Mass., a corporation of Massachusetts Filed May 29, 1967,Ser. No. 641,861 lint.. Ci. C23c 15/00 US. Cl. 20d-298 5 Claims ABSTRACTE THE DISCLSURE A sputtering apparatus with an opposing anode andsputter cathode target with an electron source behind the targetproducing an electron beam encircling the target and conveying towardsthe anode.

The present invention relates to sputtering apparatus. It is the objectof the invention to provide a highly eiiicient sputtering apparatus.

Referring now to the drawing there is shown a vacuum chamber with apumping port 12 for connection to vacuum pumping means (not shown).Within the vacuum chamber is a thermionic cathode 1li, and anode 16, asputter target 18, a target electrostatic shield located within theCrookes dark space region of the target, and a magnet 22 producing amagnetic field about the apparatus axis 24. The anode, cathode andtarget are also aligned along essentially the same axis.

A substrate to be coated is mounted on the anode at 26. However, thesubstrate can also be at the alternate locations indicated at 28 or eveneliminated since the apparatus is useful even without its coatingfunction for sputter etching of selected target materials, getterpumping and other purposes.

The various electrodes and shields are water-cooled by coolant flowingin piping 30 to reduce outgassing and promote electrical stability ofthe apparatus.

A grid electrode 32 may be provided to assure good starting of theelectron discharge from the electron source 14 at low pressures.

The various electrodes are provided with power supplies for biassing toappropriate voltage. Typical values are indicated in the drawing. Thesupplies are indicated schematically. In practice they would be outsidethe chambers and connections would be made in electrical feedthroughs.

Electrons are emitted from the thermionic filament 1S and emerge fromthe electron source 14 as an annular beam directed as indicated by thearrows E. The electrical field of the target 18 indicated by the lines34 tends to make the electron beam E go out. But this tendency iscounteracted by the magnet 22 to produce the desired resultant path.Collision of the electrons with residual'gas molecules along theelectron path produces positive ions of the gas among the collisionproducts. These ions tend to travel along the path indicated by thearrows 36. However, they are stripped from this path by the highlynegative target 18 and are attracted to the target at high velocity tosputter it. The sputtered target material will leave the target and aportion of it will be collected on the substrate at 26.

The invention provides a highly efficient production and concentrationof ions, thus allowing faster rates of sputtering and is consistent withoperation at lower pressures such as 1x10*4 torr where a lower densityof gas molecules is available for ionization and sputtering, but wheretraditional sputtering problems of contamination and diffusion areattenuated.

Patented Sept. 22, 197@ ln fundamental terms, the present inventionprovides a sputter target and means for producing electrons movingobliquely in front of and axially away from the target as indicated byarrows E. There is a prior art unit in which electrons move obliquely infront of and axially towards the target. In the prior art unit, thebasic tendency is for ions to drift away from the cathode dark space ofthe target whereas in the present invention, the tendency is for ions tomove into the dark space, thus providing an efficiency of 2-3 times thatof the prior art apparatus.

In distinctly advantageous specific embodiment of the invention theelectron beam starts in an annular form around the edge of thetarget-meaning the conical beam shown in the drawing adjacent circulartarget 18 or one or more sheet beams adjacent along edge(s) of anelongated target or other equivalents.

Advantageously, the electron emitter is located behind the target as inthe drawing and the electrons are electrostatically guided by the nestedcup-like shields 20, 21 with the inner shield 20 also serving as an arcpreventing shield for target 18.

It is desirable to provide a current regulating circuit (not shown) forthe power supply of anode 16 the limit current drawn thereby to as highas about 10` amperes.

Variations of the above described apparatus will now be apparent tothose skilled in the art. It is therefore intended that the abovedescription shall be read as illustrative and not in a limiting sense.

What is claimed is:

1. In a sputtering device the combination of a sputter target, having afront surface and a back and an annular edge and an axial frontaldirection extending perpendicular to the front surface, means forbiassing the target to a high negative potential, means including anelectron emissive source separate from said target and located in aregion behind said target for forming and directing a beam of electronsas an annular beam moving adjacent the target edge and moving obliquelywith respect to said axial frontal direction and away from the frontalsurface to converge in front of the target.

2. The apparatus of claim 1 with an anode electrode arranged in opposingrelation to the target.

3. The apparatus of claim 2 with means for supporting a substrate, to becoated by sputtered target material, located at the anode.

4. The apparatus of claim 1 wherein the said electron v forming meansare deiined by a pair of nested cup-like shields with an electronemitter therebetween.

5. In a sputtering device the combination of a sputter target, having afront surface and a back and an edge and an axial frontal directionextending perpendicular to the front surface, means for biassing thetarget to a high negative potential, means including an electronemissive source separate from said target and located in a region behindsaid target for forming and directing a beam of electrons movingadjacent the target edge and moving obliquely with respect to said axialfrontal direction and away from the frontal surface to converge in frontof the target.

References Cited UNITED STATES PATENTS 3,296,115 1/ 1967 Laegreid et al204-298 2,103,623 12/ 1737 Kott 204-298 HOWARD S. WILLIAMS, PrimaryExaminer S. S. KANTER, Assistant Examiner U.S. C1. X.R. 204--192

